Twin-wire papermaking apparatus with stock inlet passageway having straight and parallel walls

ABSTRACT

In the inlet section of a papermaking machine, stock is accelerated and passed through a relatively long and straight passageway, defined by substantially impervious walls which are substantially parallel to each other, thereby stabilizing substantially the entire flow of the suspension to move uniformly in the same direction at the same speed. A pair of forming carriers enter the inlet section, and run along the terminal sections of the walls of the passageway, capturing the stabilized suspension therebetween and carrying it out the outlet of the passageway prior to any substantial web formation and into a forming section. Water is removed from the suspension in the forming section to form a paper web.

July 9, 1974 G. T. WARD TWIN-WIRE PAPERMAKIN G APPARATUS WITH STOCK INLET PASSAGEWAY HAVING STRAIGHT AND PARALLEL WALLS Filed Feb. 28, 1972 United States Patent @fice 3,823,064 TWIN-WIRE PAPERMAKING APPARATUS WITH STOCK INLET PASSAGEWAY HAVING STRAIGHT AND PARALLEL WALLS George T. Ward, Greenwich, Conn., assignor to International Paper Company, New York, NY. Continuation-impart of application Ser. No. 796,131, Feb. 3, 1969, now Patent No. 3,645,842. This application Feb. 28, 1972, Ser. No. 230,006

Int. Cl. D21f 1/00 US. Cl. 162-301 3 Claims ABSTRACT OF THE DISCLOSURE In the inlet section of a papermaking machine, stock is accelerated and passed through a relatively long and straight passageway, defined by substantially impervious walls which are substantially parallel to each other, thereby stabilizing substantially the entire flow of the suspension to move uniformly in the same direction at the same speed. A pair of forming carriers enter the inlet section, and run along the terminal sections of the walls of the passageway, capturing the stabilized suspension therebetween and carrying it out the outlet of the passageway prior to any substantial web formation and into a forming section. Water is removed from the suspension in the forming section to form a paper web.

This application is a continuation-in-part of copending application Ser. No. 796,131, filed Feb. 3, 1969, now U.S. Pat. No. 3,645,842, issued Feb. 29, 1972.

This invention relates generally to apparatus for making paper or the like. More specifically, the invention relates to apparatus for forming a web of suitable fibers. The invention is particularly directed to apparatus for the control of the suspension of fibers as it passes from the inlet section to the forming section of the machine.

In papermaking an aqueous suspension of papermaking fibers, known as stock, is supplied to an inlet section including a chamber, known as a head box. From the head box the stock flows through an orifice, commonly 'known as a slice, into a forming section, pouring onto a moving endless foraminous forming carrier, commonly known as a wire. Water is drained from the suspension through the forming carrier, forming a web of the papermaking fibers on the carrier, the web being subsequently dried to form paper.

Certain non-uniformity of the finished paper, particularly in high speed operations, may be occasioned by aberrations in the free surface of the stock as it is moved along on the carrier into the forming section where the paper Web is formed. Such aberrations are carried on through the machine and appear in the finished paper. It has therefore proved desirable to control the free surface of the stock on the carrier. It is known to utilize a so-called twin-wire machine wherein the stock is directed from the head box as a free jet into a space between a pair of endless forming carriers. The turbulence in the exposed surfaces of the jet between the head box and the forming carriers nevertheless permits certain nonuniformity in the surface of the stock as it is deposited between the forming carriers, again producing aberrations in the paper.

It is also known to utilize a pressure forming machine wherein the forming carrier passes over a large opening at the outlet of the head box, and the stock is forced against the carrier under pressure. The water is drained from the stock in this pressure forming region to form a web on the carrier. Such systems have also included the use of a felt carrier passing into the head box and overlaying the formed web as it leaves the head box.

Although in such apparatus there is no uncontrolled free surface of the stock on the forming carrier, the stock in the head box is turbulent. This condition produces great shear forces that may interfere with the orderly formation of the web, resulting in non-uniformity.

In accordance with the present invention, the stock is stabilized, and the web is formed while keeping the stock controlled at all times from within the inlet section to the web forming section. There is no free surface of stock on the forming carriers, and substantially all parts of the stock move uniformly at the same speed in the same direction. Further the stabilized stock moving uniformly at the same speed in the same direction is placed between the forming carriers and is captured thereby. It is then carried from the inlet section between the forming carriers prior to any substantial formation of the web. To

this end the stock is accelerated in the inlet section, applying forces tending to straighten out the fibers, and the stock is then passed through a straight passageway over a relatively long distance. Thereby any great turbulence and speed differentials in the stock are damped and dissipated until the stock is stabilized and all moves in substantially the same direction at substantially the same speed without turbulence, except for such as inherently occurs along the boundary layer of the flow, adjacent the walls of the containing conduit. The stabilized flow is then passed between a pair of forming carriers moving through the terminal portion of the inlet section generally in the same direction as the stock. The stock moves uniformly in the same direction as the forming carriers as the carriers leave the enclosed inlet section and move with the stock between them into the forming section prior to any substantial web formation. The web is then formed in the forming section by removing water through both forming carriers.

It is, therefore, an object of the present invention to provide an improved apparatus for forming a paper web wherein the stock is stabilized within an inlet section and is controlled at all times from its exit from the inlet section to its formation into the web. Other objects and advantages of the invention will become apparent from the following detailed description, particularly when taken with reference to the drawings, in which:

FIG. 1 is an illustration, partly diagrammatic and partly in section, showing a papermaking machine incorporating the present invention;

FIG. 2 is an enlarged sectional view of the inlet section of the apparatus shown in FIG. 1;

FIG. 3'is a further enlarged sectional view of the seal shown in FIGS. 1 and 2; and

FIG. 4 is an enlarged sectional view of a modified form of the terminal part of the inlet section shown in FIG. 2.

In FIG. 1 there is illustrated a papermaking machine including an inlet section 10 fashioned in accordance with the present invention. The inlet section 10 has an inlet 12 for admitting a suspension of papermaking fibers and an outlet 14 for discharging the suspension. The suspension flows into the inlet 12 from a distribution system 15 which may be a conventional distribution system applying a water suspension of papermaking fibers substantially evenly distributed over the width of the papermaking machine.

As illustrated in FIGS. 1 and 2 the stock may flow horizontally in the inlet section some distance above where the paper web is to be formed. The inlet section 10 widens in a transition section 16 where the flow is turned by the curved wall sections 18 and 20 to flow downwardly through a narrowed, elongated passageway 22. Vanes 24, disposed within the transition section 16, serve to separate the flow of stock suspension into smaller streams and direct the separated flow around the bend into the straight narrow passageway 22. By breaking the stream up into smaller Patented July 9, 1974 parts and directing the individual parts, gross turbulence in the flow is prevented. The relatively long passageway 22 is formed by relatively straight wall sections 26 and 28 which form a passageway 22 of substantially constant cross section and direct the stock suspension to move in a given direction, illustrated as vertically downwardly, and over a relatively long distance sufficient to permit any eddies to be substantially damped out.

Thus, in operation, the flow of the suspension of papermaking fibers enters the inlet 12 substantially uniformly distributed cross the papermaking machine and is directed by the transition section 16 into the narrowed passageway 22. The passageway 22 has a substantially smaller cross section than the transition section 16, inherently producing a substantial increase in velocity. The acceleration occasioned by this change in cross section applies forces tending to straighten the fibers in the suspension. Acceleration changing the velocity by a factor of the order of about 2:1 has been found satisfactory. The accelerated suspension then flows through the relatively long passageway 22. As the passageway 22 has a substantially constant cross section, the flow therethrough is at a constant velocity. The suspenion becomes stabilized as the flow moves in the same direction at constant speed for a relatively long interval, whereby the suspension, as it approaches the outlet 14, is moving substantially uniformly in direction and speed. That is, all of the fibres and the suspending water move downwardly at substantially the same speed. There will, of course, be a boundary layer at the wall sections 26 and 28, as will be discussed further below.

A pair of forming carriers or wires 30 and 32 are directed into the inlet section upstream from the outlet 14. The forming carriers 30 and 32 enter the inlet section 10 through seals 34 and 36, respectively, which may comprise plastic sealing members 38 and 40, respectively. The forming carriers 30 and 32 enter the inlet section 10' over terminal wall sections 42 and 44, respectively. As shown best in FIG. 3, these terminal wall sections 42 and 44 are each preferably coated with a plastic coating 43 to alleviate wear of the forming carriers 30 and 32. The seal 34 admits the forming carrier 30 between the sealing member 38 and the plastic coating 43 on the terminal wall section 42. The seal 36 admits the forming carrier 32 between the sealing member 40 and the plastic coating 43 on the terminal wall section 44. The forming carriers 30 and 32 are bent over the wall sections 42 and 44 as they enter the inlet section 10 as this assures a smooth transition as the forming carriers enter the passageway 22. Inside the inlet sec' tion 10 the terminal wall sections 42 and 44 comprise the terminal sections of the walls forming the narrow passageway 22. These terminal wall sections 42 and 44 are substantially impervious to water, as are the straight wall sections 26 and 28, in order that the entire stabilized flow of suspension may move uniformly at the same speed between the forming carriers 30 and 32 and in the direction of movement of the forming carriers, as shown.

The suspension is captured between the carriers 30 and 32 and moves therewith out of the inlet section 10* into a forming section 46 prior to any substantial formation of a paper web. The forming section includes a plurality of seal boxes 48 and 50 disposed adjacent the sides of the forming carriers 30 and 32 opposite the suspension of papermaking fibers. The inlet of each seal box 48, 50 includes a respective foraminous carrier support 52, 54 which supports the respective carrier 30, 32 without impairing substantially the flow into the seal boxes 48 and 50. The carrier supports 52 and 54 cause the respective forming carriers to converge as they move downwardly through the forming section 46. As the suspension moves downwardly through the forming section 46 between the carriers 30 and 32, the suspending liquid is forced through the forming carriers 30 and 32 and thence through respective carrier supports 52, 54 of the respective seal boxes 48, 50 and thence through the seal boxes themselves.

The carrier supports 52 and 54 may take a number of forms. They may, as shown, comprise simple narrow bars across the forming carriers 30 and 32; however they may take complicated shapes to provide strength and relatively small disruption of drainage through the forming carriers 30 and 32. Machine direction members of the carrier supports 52 and 54 are spaced from the respective carriers 30 and 32 so as not to mark the resulting paper. The supports 52 and 54 support the respective forming carriers 30 and 32 for movement along converging paths.

The respective pluralities of seal boxes 48, 50 are disposed successively along the respective forming carriers 30 and 32 from the outlet 14 of inlet section 10 to the point or conergence of the carrier supports '52 and 54, which defines the outlet 56 of the forming section 46.

As the suspending liquid is removed from the suspension, the suspended fibers are deposited upon the respective forming carriers 30 and 32 forming a web on each forming carrier. The respective webs are joined into a single integral web by the convergence of the forming carriers 30 and 32. This convergence of the forming carriers between carrier supports 52 and 54 blocks the passage of suspension from the outlet 56 from forming section 46, permitting only the forming carriers 30 and 32 with the formed integral web therebetween to pass out of the forming section 46.

Each of the pluralities of seal boxes 48 and 50 is preferably mounted on a respective common mounting which is movably mounted so that the outlet 56 of the forming section 46 may be adjusted to accommodate different forming carriers 30 and 32 and dilferent thickness of web.

After leaving the forming section 46, the web may be further dewatered by conventional means, such as suction boxes 58, and then dried by a conventional or other dryer, not shown.

The forming carrier 30 is supported over its path by rolls 60, 62, 64, 66, 68, 70 and 72 as well as by the terminal wall section 42 and the carrier support 52. The forming carrier 32 is supported over its path by rolls 72, 74, 76, 78 and 80 as well as by the terminal wall section 44 and the carrier support 54. At least one roll in each set is a motor driven driving roll, driven by a motor 81 for driving the respective forming carriers 30 and 32 at the same linear speed. Certain of the rolls may beadjustable or biased to maintain proper tension in the respective forming carriers 30 and 32.

The formed web is confined between the two forming carriers 30 and 32 up to a sheet transfer roll 82, where the forming carrier 32 moves away from the web, leaving the web supported by the forming carrier 30. At a sheet transfer suction roll 84, the web may be transferred to a dryer fabric 86.

Various modifications may be made in the structure without departing from the scope of the invention. For example, the wall sections 26 and 28 have been described as substantially impervious, except of course as necessary to admit the forming carriers 30 and 32, and those are admitted through seals 34 and 36, respectively. On the other hand, it is within the present invention to withdraw some of the flowing suspension prior to its exit from the inlet section 10. In particular, it is sometimes desirable to withdraw at least part of the boundary layer of suspension adjacent the wall sections 26 and 28, particularly under the conditions of plug or frozen flow, as may be established by means well known in the art.

As is well known, under conditions of plug flow, the suspension moves substantially as a unitary plug, except at the boundaries of the flow adjacent the confining walls, These boundary layers are inherently fiber-free, and it is at times desirable to withdraw this fiber-free water to maintain control of the flowing suspension. This phenomenon is described in an article entitled Rheological Models and Laminar Shear Flow of Fiber Suspensions, Bugliarello and Daily. The TAPPI Journal of the Technical Association of the Pulp and Paper Industry, December 1961, Vol. 44, No. 12, pages 881-895. The articles discuss the presence of the fiber-free water and the effect of turbulence in the fiber-free water in breaking up the plug flow condition.

To alleviate problems created by the boundary layer flow, part or all of this layer may be removed by the modified structure illustrated in FIG. 4. As there illustrated, the walls 26 and 28 are made slightly pervious to the water just upstream of the forming carriers 30 and 32, and the boundary layers flow through openings 188 and 190 in Wall sections 26 and 28, respectively, into collecting boxes 192 and 194, whence the water may be disposed of as the water collected in the seal boxes 48 and 50.

The stabilized central part of the suspension is then placed upon the forming carriers 30 and 32 and is carried therebetween out of the inlet section without any substantial web formation on the forming carriers 30 and 32. The amount of suspension withdrawn in the boundary layer is negligible relative to the volume of the central flow.

One of the advantages of the control afforded by the present invention is the ability to produce a relatively square sheet. In conventional papermaking machines, the fibers are preferentially directed in the machine direction, giving the resulting paper decidedly greater strength in the machine direction. With the present invention it is possible to make the machine and cross direction strengths relatively equal by making the speed of the forming fabrics 30 and 32 substantially the same as that of the suspension. On the other hand, the present invention permits control of the relative machine and cross direction strengths by controlling the speeds of the forming carriers relative to the speed of the suspension.

The present invention is also particularly adaptable for making multilayered paper. To this end separate streams of stock may be introduced between the forming carriers 30 and 32 and processed together, as described in the aforesaid copending application Ser. No. 796,131, now US. Pat. No. 3,645,842.

The present invention also has particular application to the formation of webs of various materials. Therefore, it should be noted that the term paper as used herein is not limited to webs made from any particular fibers. In addition to the relatively short wood fibers commonly used in making paper, the present invention may utilize relatively long synthetic fibers in the formation of the web or the various layers thereof.

What is claimed is:

1. In a machine for making paper or the like, the combination comprising an inlet section having an inlet for admitting a suspension of fibers and an outlet for discharging the suspension, a pair of endless foraminous forming carriers, means for supporting said forming carriers for movement over respective paths into the inlet section, through a portion thereof and out said outlet, and means for moving each of said forming carriers over the paths at the same speed as the other and capturing suspended papermaking fibers between the forming carriers, the inlet section being provided with an exit passageway leading to the outlet, which passageway is of substantially constant cross section and is formed on two sides by a pair of walls having respective facing surfaces which are substantially straight and parallel to each other over a substantial distance up to and at the outlet, which pair of walls have respective substantially straight and parallel Wall section shaped and spaced to substantially damp out eddies and cause the entire flow of suspended fibers to stabilize and move toward the outlet and between said forming carriers uniformly in speed and direction, said forming carriers contacting said suspension downstream of said straight and parallel wall sections, said walls having respective substantially impervious terminal sections supporting respective ones of said forming carriers from their entry into said inlet section to their exit from said outlet, whereby the suspended fibers are moved from the outlet between the forming carriers prior to any substantial formation of the web; and a forming section including means positioned downstream of the outlet for removing water from the suspension through said forming carriers.

2. The combination of Claim 1 including means in said passageway walls just upstream from said forming carriers to remove at least a part of the boundary layer of flow before the suspension reaches the forming carriers.

3. The combination of Claim 1 wherein means forming said inlet section immediately upstream of said passageway define a cross section of flow through said inlet section that is substantially reduced to said uniform cross section at the beginning of said passageway.

'References Cited UNITED STATES PATENTS 3,440,136 4/ 1969 Nelson et al. 162-203 X 1,927,378 9/1933 Street 162-344 X 3,645,842 2/1972 Ward 162303 FOREIGN PATENTS 1,582,914 10/ 1969 France 162-203 S. LEON BA'SHORE, Primary Examiner R. H. TUSHIN, Assistant Examiner US. Cl. X.R. 

